FMath::IsNearlyZero

function Core Since unknown

#include "Math/UnrealMathUtility.h"

Access: public Specifiers: static

Description

Returns true if a floating-point value is within ErrorTolerance of zero. Equivalent to FMath::Abs(Value) <= ErrorTolerance.

Signature

static UE_FORCEINLINE_HINT bool IsNearlyZero(float Value, float ErrorTolerance = UE_SMALL_NUMBER)

Parameters

Name	Type	Description	Default
Value	float	The value to test.	—
ErrorTolerance	float	Maximum absolute value considered 'nearly zero'. Defaults to UE_SMALL_NUMBER (1e-8).	UE_SMALL_NUMBER

Return Type

bool

Caveats & Gotchas

• The default tolerance UE_SMALL_NUMBER (1e-8) is extremely tight. For gameplay use (e.g. checking if velocity is effectively zero), UE_KINDA_SMALL_NUMBER (1e-4) or a domain-specific epsilon is usually more appropriate.
• FVector has its own IsNearlyZero() member that checks all three components independently — prefer that over calling FMath::IsNearlyZero on each component separately.

Example

Guard a division and check if movement has stopped C++

// Avoid divide-by-zero before normalising
if (!FMath::IsNearlyZero(Magnitude))
{
	Direction = RawVector / Magnitude;
}

// Check if the character has effectively stopped
if (FMath::IsNearlyZero(GetVelocity().Size(), 1.0f))
{
	OnMovementStopped();
}

Version History

Introduced in: unknown

Version	Status	Notes
5.6	stable	—

Feedback

Was this helpful?